Field of the Invention
The present invention relates to an optical interference tomographic apparatus, and a method for controlling the same.
Description of the Related Art
Currently, an optical interference tomographic apparatus (hereinafter referred to as OCT apparatus) for performing OCT (Optical Coherence Tomography) which uses interference of light waves is widely used in diagnosis in an ophthalmology field. This OCT apparatus divides light of a low-coherence light source into measuring light which irradiates an eye to be inspected, and reference light, and irradiates the eye to be inspected with the measuring light. After this, reflected light or back scattered light of the measuring light, which is obtained from the eye to be inspected, interferes with the reference light, and interference light is obtained. A tomographic signal at some position of the eye to be inspected can be acquired from the interference light. When the eye to be inspected is scanned with the measuring light, the tomographic signal inspected. A tomographic image can be composed by an operation of making each of the obtained tomographic signals correspond to measurement positions of the eye to be inspected, respectively.
Accordingly, such an OCT apparatus has generally a scanning mechanism of the measuring light in order to photograph a broad range of the eye to be inspected. A scanning mirror is widely adopted for these scanning mechanisms, which planarly scans the eye to be inspected through an optical component arranged in an optical path. Japanese Patent Application Laid-Open No. 2012-211797 shows an example in which a galvanometer mirror is adopted for the scanning mechanism.
The scanning mechanism with the use of the scanning mirror or the like scans the measuring light while changing the angle of the scanning mirror with respect to an optical component such as a lens and a dichroic mirror which are arranged in the optical path, in this case, the incident angle of a light beam on each of the optical components results in varying according to a scanning angle. When the incident angle of the light beam such as the measuring light varies, in the case of an optical component such as the dichroic mirror, which is used for reflection or transmission, reflection or transmission characteristics occasionally vary according to the incident angle of the light beam. In addition, in the case of the optical component such as the lens which is used in the transmission, when the incident angle of the light beam varies, an optical path length of the light beam results in varying according to the curvature and the thickness of the optical component.
Furthermore, in the case of a Fourier domain type OCT apparatus which uses a plurality of wavelengths, the optical path lengths vary depending on every wavelength according to a scanned position. In the optical component such as the dichroic mirror and the lens, the dispersion characteristics according to the wavelength of the light vary, and the amount of phase shift varies depending on every wavelength. A method for correcting the dispersion characteristics includes a technique exemplified in Japanese Patent Application Laid-Open No. 2011-214968.
When the eye to be inspected is scanned with a light beam with the use of the above described configuration, the intensity and the optical path length of the light beam vary depending on every scanned position on the eye to be inspected, according to the optical component in the optical path. If this difference between the optical path lengths is large, there is a possibility that the focusing positions on the eye to be inspected vary depending on every scanned position, the contrast of the tomographic image becomes low, and layer detecting accuracy is lowered. Specifically, there is a possibility that the contrast of the tomographic image and the like is lowered according to the scanned position with the measuring light on the eye to be inspected.